The present invention relates to a combined process for separating and converting asphaltenes of high molecular weight and high softening point from heavy hydrocarbon material containing asphaltenes by a process that combines a deasphalting method to produce solid asphaltenes and a continuous coking procedure for said solid asphaltenes. The combined process converts said material into more valuable liquid hydrocarbon products of lower molecular weight and coke.
Heavy crude oils have high asphaltene content which is detrimental to further processing of these crude oils to convert them into more valuable products.
In distilling these heavy oils, it is only possible to recover about 40 to 60 weight percent of distillate and heavy gas oil, still leaving a large fraction of heavy residue with high concentration of asphaltenes, metals and sulfur. By means of solvent deasphalting using an aliphatic hydrocarbon with 5 to 12 carbon atoms in its molecule, it is possible to make a deeper cut and extract more oil and resins, thus increasing the recovery of oil products almost free of asphaltenes and having a lower metal content, which can be used as a feed to downstream refining processes, such as fluid catalytic cracking, catalyic desulfurization or the like. The metals are mainly concentrated in the precipitated asphaltenes of high softening point and high molecular weight.
In recent years, solvent deasphalting has evolved in the direction of increasing deasphalted oil yields using heavy paraffinic solvents like pentane, hexane or light naphthas. This reduces production of asphaltenes leaving a very hard material with softening point over 170.degree. C. and molecular weight over 1500. These asphaltenes have low commercial value due to high metal and sulfur content, therefore it is commercially attractive to convert them into more valuable products, increasing the amount of distillate obtained from the heavy crude oil and reducing the pilestock of low value asphaltenes.
Asphaltenes are thermal labile products that decompose when they are heated. Therefore, asphaltenes can be heated up to cracking temperature to produce distillate, gas and coke. This heating process is a coking process because the feed product is cracked to produce coke.
There are no commercial processes for asphaltene coking. Other coking technologies that could be potentially applied to low softening point asphaltenes like delayed coking require a liquid feedstock. These types of processes have severe limitations when used with high softening point asphaltenes, since these asphaltenes will start decomposing before they are melted. High softening point asphaltene decomposition usually begins at 180.degree. C. while they melt close to 300.degree. C. This puts limitation in the feeding system for any conventional coking technology, rendering it almost impossible to feed the asphaltenes to the coking unit. Therefore, application of conventional systems have been limited to asphalt containing streams coming from the bottom of vacuum residue towers in petroleum refineries.